The application is a continuation-in-part of U.S. patent application Ser. No. 08/307,849 filed on Sep. 30, 1994 in the name of Heinrich Luckhardt, which claims the benefit of PCT International Application No. PCT/EP93/00836 filed Apr. 2, 1993, and the benefit of German Application No. P4 211276.1 filed on Apr. 3, 1992. This invention relates to installation heads and, in particular, discloses an improved installation head with holding fingers that interact with an improved fastener to ensure proper alignment of the fastener from its entry into the installation head until the fastener is installed in a workpiece. The present invention is suited for use with any type of fastener, particularly pierce-type fasteners.
In the mass production of parts, fastener installation tools are commonly used to simultaneously install fasteners in, for example, a panel, as the panel is being formed in a press. The installation tool is mounted in the press and, as the press closes, the fastener is installed. The installation tool has a housing, a plunger passage, a plunger operatively mounted in the plunger passage, and a fastener feed mechanism that feeds fasteners into the plunger passage. The passage and the fastener have complementary shapes, and the plunger is adapted to drive the fastener through the passage into the panel. To assist in the initial alignment of the fastener with respect to the plunger, catches are used to hold the fastener in the passage as the fastener enters. Once the plunger contacts the fastener, the fastener either drops through to the workpiece or is temporarily held by, for example, spring-loaded detents extending into the passage.
Although the passage and fastener are configured to facilitate the proper alignment of the fastener with respect to the plunger and the panel, the fastener can become misaligned within the passage. For example, if the detents stick or fail, the fastener will cock in the passage and be misaligned when it is driven into the panel. Misalignment problems are exacerbated when the installation tool is not vertically oriented with respect to the workpiece. Non-vertical orientations are very common. As should be appreciated, misalignment can result in faulty installations, damage to the part, and damage to the installation tool.
The installation head illustrated in U.S. patent application Ser. No. 08/307,849 overcomes the above problems. However, it does have disadvantages. First, the fingers which hold the fastener against the plunger do not hold the fastener at the critical point of contact with the workpiece. It has been found by Applicant that it is important to hold the fastener until at least the installation end of the fastener engages the workpiece so that the fastener is being held between the plunger and the workpiece. At this point, the fingers can be removed and proper installation will be ensured. Additionally, Applicant has found that in many applications, it is important that the fingers maintain guiding contact with the fastener until the fastener is completely installed in the panel. Neither of these holding techniques can be achieved by the disclosed invention because the fingers are cammed away from the fastener through contact with the panel surface. By definition, the fingers release the fastener prior to the fastener making installation contact with the panel. Although this distance is slight, it is sufficient to result in misalignment of fasteners. This is particularly true, since the panel surface is required to act as a cam surface when, in fact, it is not designed to be a cam surface. Therefore, any restriction of the fingers can result in the fingers not moving properly and resulting in a cocked fastener at the critical installation point. It should be appreciated that any tilting of the fastener at installation can result in an improper installation of the fastener.
Another disadvantage to the installation head disclaimed in the co-pending application is the potential marring of the panel surface due to the fingers being cammed against the surface at installation. This marring can be unacceptable in many applications, resulting in rejected panels and increased manufacturing costs.